The present invention relates to a copying machine and, more particularly, to a transfer type electrostatic copying machine which employs a total surface exposure system for high speed copying, employing an endless belt having one outwardly facing photosensitive surface which can be repeatedly rotated for successively copying several sizes of copy-paper sheets.
In a copying machine of a similar character, an image of an original to be copied is projected onto a charged photosensitive body so as to form a charged latent image thereon corresponding to the image on the original, the latent image being developed, for example by applying toner, for transfer onto a copy-paper sheet by a suitable means so as to obtain a copy of the original image thereon.
In the conventional copying machine of the above construction, a drum type photosensitive body is widely used. This type of copying machine employs the so-called slit scanning exposure system, in which the image to be copied is formed on the photosensitive surface of the drum by slit exposure while the photosensitive drum is being rotated, as a platform for the original document or, alternatively as a light source is being moved. Although it may be possible to effect high speed copying by the above means with less time required for printing a single copy and for obtaining the first copy the system is disadvantageous in that the second and further copies require a longer period of time between copying operations because image exposure can not be made while the platform or light source is returning to its initial position. Thus, reduction of time per copy is limited, without the possibility of high speed copying.
On the other hand, in some of the conventional copying machines, a flexible endless belt having one outwardly facing photosensitive surface is used, the endless belt being suspended between two rollers with a flat photosensitive surface defining a maximum paper size to be processed provided on both the top and bottom portions of the belt so that two copies can be obtained for each rotation of the belt. The disadvantage of the conventional copying machine of the above described type is that, besides being unable to effect high speed copying, the endless belt must travel the same distance as the maximum paper size, even for copying an image of minimum paper size, and in copying a single copy sheet the photosensitive surface of the belt is subjected to extreme fatigue resulting in short life, since the belt always makes one full rotation, necessitating the repeated use of the same photosensitive surface.
In order to achieve high speed copying in a copying machine employing a photosensitive endless belt, a high speed copying machine is proposed by U.S. Pat. No. 3,661,452 in which a total surface momentary exposure system with a jointless endless belt and flash discharge tubes for illumination is employed. In reality, however, considering the fact that a photosensitive endless belt without a joint is difficult to massproduce, with consequent high cost, and in view of the fact that the only photosensitive body readily available is one in the form of a long sheet produced by the continuous coating technique, the above ideal high speed copying machine is actually impractical. Furthermore, in the above copying machine, the photosensitive endless belt must make one complete rotation in copying a single copy sheet, necessitating the repeated use of the same image forming surface, with extreme fatigue thereof and short life of the photosensitive surface. Moreover, in the above copying machine the time required for the exposure portion to pass along the surface of the endless belt is long, being limited by the dimension of the maximum paper size in comparison with the slit scanning exposure system, so that with respect to high speed copying, the above copying machine has a serious disadvantage in the time required for making a single copy and for obtaining the first copy in a continuous copying process.
From the above description, it will be seen that in order to meet the requirements for higher copying speed, a copying machine employing a jointless photosensitive endless belt for high speed copying at a rate at least equivalent to the total momentary exposure system will have to be devised, in which the high speed copying at a rate equivalent to the slit scanning exposure system is attained in copying a single copy, with similar high speeds for Letter size, Legal size and Computer size copy paper sheets, which are all widely used in the United States. Furthermore, the life of the photosensitive surface should be extended, through approximately uniform use of the entire surface-thereof.